Theory of Ga, N and H terminated GaN (0001)/(0001) surfaces

We present a theoretical study of atomic structures, electrical properties and formation energies for a variety of possible reconstructions with 1x1 and 2x2 periodicity of the GaN(0001) and (000 (1) over bar) surfaces. We find that during MBE growth in the (0001) direction 2x2 structures become stable under N rich growth conditions while Ga rich environment should yield structures with 1x1 periodicity. Considering MBE growth on (000 (1) over bar) surfaces, among the investigated structures only those with 1x1 periodicity are predicted to be stable. During MOCVD growth, where H terminated surfaces may occur, only structures with 1x1 periodicity are found to be stable for both growth directions.